The present invention relates to a vertical take-off and landing, aerodynamically self-sustained horizontal flight hybrid aircraft.
As is well known, a main advantage of vertical take-off and landing aircraft, also known as VTOL, is the capability of reaching almost anywhere, regardless of the size of the landing area. This advantage is counterbalanced by the high operating costs of the existing VTOL technology, particularly helicopters, with respect to the other vehicles and transportation systems. Increased costs are due to the very high amount of power necessary to sustain the helicopter during its horizontal flight, in view of the absence of aerodynamic sustaining thrust of the fixed wings that are provided in traditional horizontal flight (HF) aircraft.
Two models of aircraft are provided with interchangeable integrated VTOL-HF characteristics, namely the Harrier and the V-22 Osprey. The Harrier is a military jet aircraft made in Great Britain by a British Aerospace and McDonnel Douglas joint-venture. The Osprey is a military turbo-prop aircraft, providing a tiltable rotor-engine group made in the United States by Bell Textron and Boeing.
Harriers are provided with VTOL capability by rotating downward the thrust of its main jet engines during the take-off and landing. Ospreys rotate the main engines at the ends of the wings to provide the relevant thrust in the VTOL and HF modes. Thrust for the Osprey is based on a compromise between big propellers and rotor blades since the engines work in both the HF and VTOL modes.
Both solutions concern aircraft particularly designed to be used as VTOL-HF aircraft. However, the main engines are sized on the basis of the maximum thrust necessary for VTOL, with a consequent impact on the operating costs.
A hydraulic drive for synchronously driving a pair of interleaved propellers in a conventional HF aircraft is disclosed in Sager, U.S. Pat. No. 5,810,289. However, the hydraulic system does not operate so that hydraulic power is alternately provided to different types of propulsion systems that separately provide propulsion for VTOL and HF modes of operation and thus is not sufficiently robust for VTOL-HF operation.
A main object of the present invention is that of realizing a new vertical take-off and landing, aerodynamically self-sustained horizontal flight hybrid aircraft (VTOL-HF) with an improved propulsion system that avoids the problems of the prior art.
The solution suggested according to the present invention is an aircraft with a fuselage with a pair of wings providing lift during horizontal flight, a main engine carried by the fuselage, a rotor system on the nose of the fuselage providing lift during vertical take-off and landing, the rotor system having at least one rotor that is structured and arranged to be stowed in the fuselage during horizontal flight, a first pair of ducted fan propellers mounted on the wings, a second pair of ducted fan propellers mounted adjacent to a tail of the fuselage, the second pair of ducted propellers being tiltable to vary a direction of thrust, a hydraulic system powered by the main engine, the hydraulic system being connected to and generating propulsive hydraulic power for the rotor system and the first and second pairs of ducted fan propellers, and a control system for controlling the hydraulic system. The control system provides propulsive hydraulic power to the rotor system and to the second pair of ducted fan propellers during vertical take-off and landing and not to the first pair of ducted fan propellers during vertical take-off and landing and provides propulsive power to the first and second pairs of ducted fan propellers during horizontal flight and not to the rotor system during horizontal flight.